It is impossible not to be fired up by Kurt Kuenne’s incendiary cri de coeur, “Dear Zachary: A Letter to a Son About His Father.” At once a personal documentary about the murder of his best friend and a polemical rant against the Canadian justice system for coddling a dangerous sociopath, it wants to provoke outrage.

On Nov. 5, 2001, Mr. Kuenne’s oldest friend from childhood, Andrew Bagby, a doctor doing his residency in Latrobe, Pa., was shot to death in a parking lot. The killer, Shirley Turner, Andrew’s mentally unstable, Canadian-born ex-girlfriend, immediately fled the United States to live in St. John’s, Newfoundland, where she successfully fought attempts at extradition. Pregnant with Andrew’s child at the time of the killing, she gave birth to a baby boy, Zachary, on July 18, 2002.

Begun before a second tragedy altered its direction, “Dear Zachary” was conceived as a cinematic scrapbook for Zachary consisting of home movies Mr. Kuenne made with Andrew and loving reminiscences by Andrew’s family and friends, all of whom attest to what a wonderful, generous, life-loving fellow he was.

After Andrew’s death, his parents, David and Kathleen, sold their house in Sunnyvale, Calif., and moved to Canada to be near their grandson. Fearing that the boy was in danger from his mother, they waged a protracted custody battle with Shirley. To their horror, she was freed on bail pending extradition, on the ground that she posed no danger to society because she had killed the one person she wanted dead.

Suffice it to say, their fears were justified; the other shoe dropped. How and when, I leave you to discover for yourself.

DEAR ZACHARY

A Letter to a Son About His Father

Opens on Friday in Manhattan.

Written and directed by Kurt Kuenne; music by Mr. Kuenne; released by Oscilloscope Pictures. At Cinema Village, 22 East 12th Street, Greenwich Village. Running time: 1 hour 35 minutes. This film is not rated.